In a helicopter rotor system, a flapping hinge offset refers to a design feature where the rotor blades are not perfectly aligned with the rotor hub's axis but are offset at a slight angle. This offset allows the rotor blades to flap or move up and down as they rotate, and it plays a significant role in the rotor's aerodynamic performance and stability.

The flapping hinge offset creates a hub moment. When the rotor blades flap up or down due to the offset, they produce a moment (a turning force) at the rotor hub. This moment can affect the overall balance and behaviour of the rotor system and, consequently, the helicopter's flight characteristics and is expressed as % of rotor radius.

The greatest amount of control power is provided by the hingeless rotor. Rather than flapping on a hinge, the blade flexes along its span. The point of flexure is equivalent to a hinge offset of as much as 17% of the rotor radius.